This invention concerns the fabrication and use of polyaryletherketone-based thermoplastic materials in the fabrication of oil field tools employed in downhole logging applications. By way of background, downhole logging tools are exposed to difficult environmental conditions. The average depth of wells drilled each year becomes deeper and deeper, both on shore and off shore. As the wells become deeper, the operating pressures and temperatures become higher. The open or uncased hole involves the cutting of a circular well borehole through the subsurface formations. After the drill bit has passed through each strata, it leaves a fairly rough, even abrasive surface. While the abrasive nature is reduced by the accumulation of a mud cake on the sidewall, the repeated travel of a logging tool along the well borehole produces abrasive wear. In addition, they are more often than not inclined from the vertical which leads to a substantial amount of abrasive wear on the logging tools. Logging tools are lowered into a well borehole, moved to the very bottom of the well, and then retrieved. This traverse of the full length of the well exposes the logging tool to abrasive contact with the open hole.
Drilled wells can be extremely aggressive environments. Boreholes are often rugose and tend to be abrasive. Drilling muds, which are used to facilitate drilling, contain chemical additives which can degrade non-metallic materials. They are highly caustic with a pH ranging as high as 12.5. Other well fluids may include salt water, crude oil, carbon dioxide and hydrogen sulfide which are corrosive to many materials.
Downhole conditions progressively become more hostile as depth increases. At depths of 5,000 to 8,000 meters, bottom hole temperatures (BHT) of 260.degree. C. and pressures of 170 MPa are often encountered. This exacerbates degradation of exposed logging tool materials.
These deep well conditions of high pressure and high temperature (HPHT below) damage the external or exposed logging tool components. Internal electronics need to be protected from heat and external housings need to be upgraded. The most vulnerable materials are the plastic and composite materials which are exposed to caustic drilling mud and other corrosive well fluids. Some tools, such as those making electrical induction and magnetic resonance measurements, require these non-conductive, non-magnetic materials of construction in order to function properly. This requires materials which are essentially transparent to electromagnetic radiation and have magnetic permeability of 1.
Ceramics generally are too brittle, i.e., a sharp impact may fracture the ceramic. The present disclosure sets forth a composite material system which is formed into the shell defining a downhole logging tool, and more particularly one which can operate at the prevailing BHT of 260.degree. or greater. It enables the construction of an elongate cylindrical sleeve and connected, end located subs which comprises the major portion of the housing, as well as other non metallic parts. The completed tool housing, and the contents within that housing are thus protected. On the interior, a pressure balance typically is achieved by raising the interior pressure inside the tool to approximate that on the exterior. Deep wells encounter pressures as high as 170 MPa or higher.
Conventional plastics such as epoxies and phenolics perform adequately in conditions up to about 180.degree. C. and 100 MPa. Under more extreme conditions however they fail prematurely. Many alternative materials have been evaluated and rejected for various reasons. For example, polyimides, polyetherimide ("ULTEM"), and polyamideimide ("TORLON") are well known for their excellent durability at high temperature. They, too, fail however in well fluids because their imide and amide linkages are subject to rapid hydrolytic degradation at high pH. Polyphenylene sulfide is water resistant but its crystalline melting point, 260.degree. C., is too low for this application.
One class of material, polyaryletherketones, meets the demanding thermal and chemical requirements for this application. It has the desired high pressure, high temperature (HPHT) performance characteristics, and is also impervious to chemical attack by well and formation fluids. It provides structural rigidity and strength at HPHT conditions even in the presence of chemically active materials. For instance, there is always the risk of H.sub.2 S invasion in a deep well. The shell of the subject invention is impervious to H.sub.2 S. Moreover, it is both tough and resilient so that abrasive contact during movement in the well borehole does not damage or otherwise harm the apparatus. Finally, the apparatus is well able to enclose all the sensing components of an induction logging tool. The novel shell is substantially transparent to signal transmission from the logging tool and response from the formation.
The present disclosure includes a sleeve which defines the housing for a logging tool supported both on a drill stem and wireline. Successful downhole housing shells, end connected subs, and a variety of other parts are made of polyaryletherketone based thermoplastic materials to operate at HPHT conditions.